In the United States, there are currently as many as 300,000 coronary artery bypass graft (CABG) procedures performed on patients annually. Each of these procedures may include one or more graft vessels which are hand sutured. Until recently, coronary artery bypass procedures have been performed with the patients on cardiopulmonary bypass whereby the heart is stopped with cardioplegia and the surgery is performed on an exposed, stationary heart.
The vast majority of CABG procedures performed currently are accomplished by opening the chest wall to gain access to the coronary vessels. Through the use of heart lung bypass machines and a drug to protect the heart muscle, the heart is stopped and remains still during the procedure. In this setting, the surgeon has ample time and access to the vessels to manipulate hand suturing instruments such as forceps, needle holders and retractors.
However, with increasing costs of hospital stays and increased awareness by patients of other minimally invasive surgical procedures, interest in developing a minimally invasive CABG procedure is increasing. Hospitals need to reduce costs of procedures and patients would like less post-operative pain and speedier recovery times.
In the past, two significant developments in the technology played a major role in advancing the whole area of cardiac surgery. The heart-lung machine was invented in the 1950's but underwent significant improvement in design to become a reliable clinical device in the 1960's. The heat-lung machine allows the surgeon to take the heart out of the blood circulation system to work on it in isolation.
The second major development was in myocardial protection. When the heart was isolated from the circulation, it was no longer perfused. After twenty to thirty minutes of ischemia, irreparable damage occurred and no matter how good the repair, the heart function was frequently inadequate to allow the patient to survive. Cardioplegia, a solution which is generally cold and high in potassium, changed everything. This development occurred in the 1970's. This allowed very satisfactory protection of the heart so the surgeon could perform an unhurried repair and still expect the heart to work afterward.
A secondary consequence of these developments was the decline in interest in technology to facilitate heart surgery. When speed of the surgery was initially of utmost importance, all sorts of developments were proposed to speed surgery. Therefore, the art in the 1960's and 1970's contained numerous examples of such devices.
Now with an increased incentive to reduce costs, there is a renewed interest in redesigning cardiothoracic procedures. A few pioneering surgeons are now performing minimally invasive procedures whereby the coronary artery bypass is performed through a small incision in the chest wall. There are some surgeons that believe that the best way to perform a minimally invasive coronary artery bypass procedure is to perform the procedure on a beating heart, i.e., without heart-lung bypass and cardioplegia. This minimizes the time it takes to perform the procedure and reduces the cost of the operation by eliminating the heart lung bypass machine.
In the case of minimally invasive procedures on a beating heart, the surgeon starts by making a mini-thoracotomy between the fourth and fifth ribs and, sometimes, removing the sternal cartilage between the fourth or fifth rib and the sternum. The space between the fourth and fifth ribs is then spread to gain access to the internal mammary artery (IMA) which is dissected from the wall of the chest. After dissection, it is used as the blood supply graft to the left anterior descending artery of the heart (LAD). Below the IMA lies the pericardium and the heart. The pericardium is opened exposing the heart. At this point, the LAD may be dissected from the fissure of the heart and suspended up with soft ligatures to isolate the artery from the beating heart. Some companies are making a special retractor to gently apply pressure to the heart muscle to damp the movement right at the LAD. A small arteriotomy is performed in the LAD and the graft IMA is sutured to the LAD.
Traditionally, to gain access to the cardiac vessels to perform this procedure the sternum is sawn in half and the chest wall is separated. Although this procedure is well perfected the patient suffers intense pain and a long recovery.
Until recently all bypass graft procedures have been performed by hand suturing the tiny vessels together with extremely fine sutures under magnification. The skills and instruments required to sew extremely thin fragile vessel walls together have been perfected over the last twenty years and are well known to the surgical community that performs these procedures.
In the `open chest` surgical setting, the surgeon has adequate access and vision of the surgical site to manipulate the anatomy and instruments.
The push for less invasive surgical approaches is fueling interest in many areas that were abandoned long ago--including that of coronary fastening and valve replacement. The inventors have thus identified a need for a device and a method to perform CABG surgery on a beating heart.
Some surgeons are attempting minimally invasive CABG procedures using femoral artery bypass access rather than opening the chest for bypass via the aorta. However, since use of cardioplegia requires additional support and expense during the anastomosis procedure, the inventors believe that it is best to attempt to fasten the anastomosis while the heart is beating. However, this procedure when performed with a hand suturing technique is very imprecise due to the translation of movement from the beating heart to the suspended artery. This may cause imprecise placement of the suture needles. Any imprecise placement of the sutures may cause a distortion of the anastomosis which may cause stenosis at this junction. The sutures used for this procedure are extremely fine (0.001" in diameter) and are placed less than 1 mm apart.
As one can imagine it is difficult enough to place suture needles the size of a small eyelash into a vessel wall with placement accuracy of better than 1 mm. To accomplish this feat of precision on a moving target is extremely difficult. To make matters worse, the site is often bloody due to the fact that the heart has not been stopped.
Therefore, there is a need for a means and method which permits the forming of a precise anastomosis without requiring the stopping of a beating heart. Still further, there is a need for performing such an anastomosis in a minimally invasive manner.
The current method of hand suturing is inadequate for the following reasons:
On a beating heart it may be difficult to place the sutures with the position precision required. In a beating heart procedure the surgeon can attempt to minimize the deleterious effects of the movement by using suspension or retraction techniques. However, it is impossible to isolate all movement of the vessel during an anastomosis procedure.
Methods that attempt to stabilize and isolate the artery from the movement of the beating heart can damage the vessel or cause myocardial injury (MI).
In addition to the problem of placing sutures accurately one must make an incision through the artery wall to open the artery. This too is a delicate procedure even on a still heart because the incision must be of a precise length. It is also critical to not penetrate the back wall or side wall of the vessel which will lead to complications. The placement of the initial incision is of paramount importance. The surgeon must pick a suitable location free from calcium deposits, fat and side branches.
Without cardioplegia, one must also provide blood flow to the heart muscle while the heart is beating, therefore, after the initial arteriotomy, the surgical field is very bloody and obscured.
Access to the heart vessels other than the LAD will be extremely difficult with minimally invasive hand suturing due to the anatomical location of the posterior wall of the heart.
Although minimally invasive CABG procedures are taking place now with sutured anastomosis they require superlative skills and are therefore not widely practiced.
One of the most vexing problems is that of adequate access. The procedure takes place through an access site created between two ribs. The ribs cannot be spread too far without risk of breaking and the heart lies deep within the chest. The access is through a small, long, dark tunnel. The surgeon must then manipulate his tools down this tunnel without obscuring his vision.
If special tools are constructed to allow the surgeon to be able to hold suture needles on the end of a long instrument, the added length of the tool only amplifies any inaccurate manipulation. The same holds true for any special suturing devices contemplated.
If the sutures are not placed correctly in the vessel walls, bunching or leaks will occur. In the minimally invasive procedure this is disastrous, usually resulting in the conversion to an open chest procedure to correct the mistake. Any rough handling of the vessel walls is detrimental as inflammation can cause further postoperative complications.
The anastomosis must seal leak tight to prevent exsanguination. Therefore, any improvement over sutures must provide a leak free seal in a very confined space, yet should provide proper flow areas in the vessel after healing is complete.
As is apparent from the above discussion, it is necessary to find a way to control the beating heart movement of the vessel while performing the anastomosis in such a way that still allows for exact placement of the fastening means.
While the art contains disclosures of several devices that are used to join blood vessels, these devices are primarily directed to an end-to-end anastomosis, which is inadequate for CABG procedures. Furthermore, the techniques disclosed in the prior art often require the vessels to be severely deformed during the procedure. The deformation may be required to fit the vessels together or to fit a vessel to an anchoring device. One cannot just slit the tissue and pull it through a ring to anchor it on a flange. Pulling or stretching the vessel walls produces a very unpleasant and unexpected result. Vessel walls are made of tissue fibers that run in the radial direction in one layer and the longitudinal direction in another layer. In addition the elasticity of the tissue fibers in the longitudinal direction is greater than those that run radially. Therefore, the tissue will not stretch as easily in the radial or circumferential direction and results in a narrowing or restriction when pulled or stretched in the prior art devices. Vessel walls also have a layer of smooth muscle cells that can spasm if treated harshly. Such manhandling will result in restrictions and stenotic junctions because the vessel walls will react poorly to being treated in such a rough manner and the stretching of the vessel wall will telegraph up the vessel wall due to the high radial stiffness of the vessel structure, causing restrictions and spasms in the vessel wall. The prior art fails to teach that the vessels are living tissue and must not be made to conform to rigid fitting-like shapes. Therefore, there is a need for an anastomotic technique that permits handling of blood vessels in a manner that is not likely to cause those blood vessels to react poorly.
Additionally, prior art systems fail to teach methods of ensuring hemostasis so as not to have leakage under pressure. It is noted that mechanical devices used to join blood vessels are extremely difficult to seal. No attempt has been made in the prior art to include a hemostatic medium in conjunction with an anastomotic device. Prior art devices are directed to accomplishing hemostasis through excessive clamping forces between clamping surfaces or stretching over over-sized fittings.
In order to effect good healing, healthy vessel walls must be brought into intimate approximation. This intimate approximation is now accomplished by the skilled hands of a surgeon with sutures. A vascular surgeon is taught how to suture by bringing the vessel edges together with just the right knot tightness. Too loose and the wound will leak and have trouble healing causing excessive scar tissue to form. Too tight will tear through the delicate tissue at the suture hole causing leaks. The key is to bring the edges together with just the right amount of intimate approximation without excessive compression.
It must be further noted that the junctions taught in the prior art are not anatomically correct both for blood flow and for healing. A well made anastomotic junction is not made in a single plane and should accurately follow blood vessel geometry. The junction is more of a saddle shape, and the cross section is not necessarily a circle. The junction where the vessel units join is not a constant cross section angle, but an angle that varies continuously throughout with respect to any linear reference. In addition, the length of the junction should be many times the width of the opening in order to assure a low blood flow pressure gradient in the junction and to assure a proper flow area. In fact, the best results are obtained if the confluence area is actually oversized. The prior art junctions do not account for such flow characteristics and parameters and are thus deficient. Therefore, there is a need for an anastomotic technique which can establish proper flow characteristics and parameters and that accurately preserves blood vessel geometry, specifically the plural planar nature in which the junction occurs. Furthermore, most anastomoses are made between vessels that are not similar in size. It is therefore necessary to provide a means and method which allow for the accommodation and joining of dissimilarly sized vessels.
In addition, the inventors have found through post surgical follow-up that the supply vessels grow in diameter to accommodate their new role in providing oxygenated blood to the heart; therefore, there is a need to provide an oversized junction to accommodate any increase in the dimension of the graft vessel size. With a rigid ring that is a singular circular cross section of the graft, the fitting does not allow the vessel to provide this increase in flow as the vessels expand to meet the needs of the heart muscle. Still further, the inside lining of the vessel walls (intima) should make contact with each other to have proper healing. The walls of the vessels must come together with just the right amount of approximation to promote good healing. If the incised edges are too far apart scarring will occur causing restrictions. The walls cannot be compressed between two hard surfaces which will damage the vessels. The prior art teaches plumbing-like fittings clamped onto vascular structures. However, clamping and compressing the vessel walls too tightly will cause necrosis of the vessel between the clamps. If necrosis occurs the dead tissue will become weak and most likely cause a failure of the joint. Still further such rings and tubes used to clamp vessels together do not follow the correct anatomical contours to create an unrestricted anastomosis. Failing to account for the way healing of this type of junction occurs, and not accounting for the actual situation may cause a poor result. A suture technique has the advantage of having the surgeon making on-the-fly decisions to add an extra suture if needed to stop a leak in the anastomosis. In a mechanical minimally invasive system it will not be possible to put an `extra suture throw` in so the system must provide a way to assure complete hemostasis. Being a mechanical system the approximation will not be 100% perfect. And since the design errs on the side of not over-compressing the tissue there may be very small areas that may present a leak between the edges of the vessel walls. Accordingly healing with prior art techniques using mechanical joining means is not as efficient as it could be. Therefore, there is a need for an anastomotic technique that accounts for the way healing actually occurs and provides proper structural support during the healing process.
When vascular integrity is interrupted the body quickly reacts to reestablish hemostasis. Circulating blood platelets are quickly mobilized to the injury site and initiate and support the coagulation sequence that leads to the formation of a fibrin plug at the site of injury. Large breaks in vessel walls which are under pressure cannot be effectively sealed by platelets and fibrin without a substrate to collect on. It is critical that the junction of an anastomosis bring two healthy vessel surfaces in close approximation to provide an optimal region for vessel repair and healing, minimizing the distance between healthy endothelial cells on either side of the junction. This allows for the natural control processes which prevent platelet aggregation from extending beyond the area of injury. A more detailed description of the clot limiting process and the healing process can be found in various reference texts, such as "Coagulation: The Essentials", by Fischbach, David P and Fogdall, Richard P, published by Williams and Wilkins of Baltimore in 1981, the disclosure of Chapter 1 thereof being is incorporated herein by reference.
Still further, some vessels are located or sized in a manner that makes placing elements thereon difficult. In such a case, the fewer elements used to perform an anastomosis the better. Therefore, there is a need for a means and a method for performing an anastomosis that can be effected without the need of a hemostatic medium.
Many time when a CABG operation is undertaken, the patient has multiple clogged arteries. At the present time, the average number of grafts is 3.5 per operation. When multiple grafts are performed, there is sometimes the opportunity to use an existing or newly added supply vessel or conduit for more than one bypass graft. This is known as a jump graft, whereby the conduit, at the distal end thereof is terminated in a side-to-side anastomosis first, with an additional length of conduit left beyond the first junction. Then, an end of the conduit is terminated in an end-to-end junction. This saves time and resources and may be necessary if only short sections or a limited amount of host graft material is available.
At the present time, existing means and methods of performing an anastomosis do not permit the formation of multiple anastomotic sites on a single graft vessel such at both proximal and distal ends. Thus a surgeon will have to use multiple tools to perform multiple anastomoses. This will be either impossible or very expensive.
Therefore, there is a need for a means and a method for performing an anastomosis which will lend itself to efficient and cost-effective multiple by-pass techniques.
Therefore, there is also a need for a means and a method for performing an anastomosis which will lend itself to efficient and cost-effective jump graft techniques.
As discussed above, performing a sutured anastomosis in a minimally invasive manner while the patient's heart is beating requires an extremely high degree of dexterity. Any instrument used in such a procedure must therefore be as easy and efficient to use as possible whereby a surgeon can focus most of his attention on the anastomosis site. The instrument should thus reflect the above-discussed needs as well.
Still further, any instrument used in such a procedure must be amenable to efficient manufacture.